1. Field of the Invention
The present invention relates to machine vision. More particularly, this invention relates to imaging by artificial means (i.e., by or with the aid of man-made imaging devices) which have an objective lens receiving light and passing this light along an optical pathway to or through a focal plane at which is located a partially reflective surface. Accordingly, this invention relates to optical observation apparatus and methods in which an objective lens collects light and passes this light toward a focal plane at which is located a surface which is at least partially reflective.
2. Related Technology
Machine vision devices generally include an objective lens which receives light from an object or scene to be imaged, and which passes this light along an optical pathway to or through a focal plane. Some of these devices may have a light-responsive device, such as a CCD, disposed at the focal plane in order to respond electronically to the incident light. Thus, an electronic signal is created by the incident light, and can be used to create an image or may be recorded for later use in creating an image, or for display, for example. The artificial device, such as a CCD, disposed at the focal plane of the imaging device provides a surface which is at least partially reflective.
Alternatively, a man-made imaging device may have a reticule plate at the location of the focal plane, which provides a pattern focused at infinity, and which is seen by a human observer superimposed on the viewed object or scene when the device is used to bring light to the eye of the human observer. In such cases, both the reticule plate and the retina of the human observer may define surfaces which are at least partially reflective, and which are located at focal planes along the optical pathway of the device. Additionally, some artificial imaging devices may bring light to only a focal plan defined by the retina of a human user, and may not define any internal focal planes at which a surface which is at least partially reflective is disposed. Nevertheless, in such devices, the retina of the human observer when using such a device provides a surface located at a focal plane for light received via the device, and which is located at a focal plane for this light (even though the focal plane in not in such a case located within the device itself).
Examples of devices of the above-describe characters are seen in everyday experience. For example, the common VHS or 8 mm video camera has an objective lens and a CCD which defines a surface which is at least partially reflective and at a focal plane. A pair of binoculars when used by a human to observe a distant scene, or a microscope used to observe a close scene (i.e., one of small size in the case of the microscope) also has an objective lens and a surface which is at least partially reflective (i.e., the retina of the user), and which is located at a focal plane.
In each case explained above, and in other cases where an objective lens provides a focal plane, and a surface which is at least partially reflective is located at this focal plane, a common problem in artificial imaging, whether it be of the kind which provides an electronic signal for producing an image, or of the type which augments the natural human vision (such as a telescope, binocular, or microscope) is that at least some light is reflected from the partially reflective surface at the focal plane and returns outwardly of the device to the scene or object being viewed or imaged.
In some instances, it is very undesirable to have light reflected from an observing instrument returned to an object or scene being imaged or viewed. For example, in some chemistry experiments involving chemo-luminescence, a chemical reaction results in the production of light, and the quantity or time-rate of production of this light may provide an indication of the rate of the chemical reaction. Another example is provided by particle physics in which the light produced by particle interactions with one another or with an indicator medium is of importance in detecting the fact of or the nature of such particle interactions, or their path in a magnetic or electric field, for example. In such cases, and others, the reflection of light from an optical observation instrument back into the scene being viewed or back to an object being viewed can be very detrimental.